Disc brake

ABSTRACT

A disc brake and an adjuster system for a disc brake. The adjuster system may include a piston, a chamber, and a wear adjustment mechanism. The wear adjustment mechanism may be located within the chamber. The chamber may contain lubricant for lubrication of at least part of the wear adjustment mechanism.

TECHNICAL FIELD

The present invention relates to a disc brake. More particularly, butnot exclusively, the present invention relates to an adjuster system forinstallation in a brake pad, for adjusting the position of a brake padrelative to a brake disc so as to maintain a suitable running clearancebetween the brake pad and the brake disc.

BACKGROUND

Many brakes, for use on heavy vehicles such as trucks and buses, have anadjuster mechanism to set the position of brake pads having frictionmaterial relative to a brake rotor, to account for wear of the frictionmaterial and the rotor in brake use. These adjuster mechanisms rely onpredetermined levels of friction at multiple locations for correctfunction and are lubricated, e.g., by use of grease, to achieve thesefriction levels. Examples of such locations are one-way and frictionclutches. The viscous nature of grease means that it tends to adhere tolocations where lubrication is needed, but can migrate to otherlocations within the disc brake where it is not required, where itspresence is potentially harmful.

Further, over the lifetime of an air disc brake, the migration of suchlubrication and/or its breakdown may cause deterioration of the adjusterfunction. Adjuster mechanisms are typically not an end-user serviceableitem, so in the event of adjustment ceasing to function as required, thedisc brake will require replacement.

The present invention seeks to overcome or at least mitigate theproblems associated with the prior art.

SUMMARY

A first aspect of the invention provides an adjuster system for a discbrake, the adjuster system comprising: a piston for applying anactuating force to a brake pad and being extensible to adjust therunning clearance between a brake disc and the brake pad; a chamber; anda wear adjustment mechanism located within the chamber, for adjustingthe extension of the piston, wherein the chamber is configured tocontain lubricant for lubrication of at least part of the wearadjustment mechanism, and inhibit lubricant from migrating away from theat least part of the wear adjustment mechanism.

As the lubricant is inhibited from escaping from a defined location, itis restricted from migrating to other areas of the disc brake, reducingwear of the components of the adjustment mechanism, and extending thelife of a disc brake comprising this adjuster system. If the lubricantis grease or a lubricating oil, a higher quantity of lubricant can bemaintained near the parts of the wear adjustment mechanism needinglubrication, such as the wrap spring and/or friction clutch plates.Thus, should there be a degradation or escape of the lubricant overtime, a greater amount of lubricant will nevertheless remain in contactwith the parts requiring lubrication.

The chamber and/or the wear adjustment mechanism may comprise a radialstep arranged to define a barrier to inhibit the escape of lubricant inan inboard or outboard direction.

As a disc brake is mounted in a fixed orientation on a vehicle,provision of a radial step tends to inhibit the escape of at least aportion of lubricant under gravity and may help to create a moretortuous path out of the chamber for lubricant in the event of lubricantbeing dislodged by virtue of the disc brake being subjected tovibration, jolts or the like. The radial step may advantageously extendaround a complete circumference, such that a barrier exists irrespectiveof the orientation of the disc brake on a vehicle.

The chamber and/or the wear adjustment mechanism may comprise first andsecond opposed interface surfaces having a spacing sufficiently smalltherebetween so as to act a barrier to inhibit the escape of lubricantin an inboard or outboard direction.

The first and second opposed interface surfaces further improve thecontainment of lubricant within the chamber. The surfaces may beradially opposed or axially opposed. The spacing required may be largerfor relatively viscous lubricants such as grease, and a closer fit forthinner, freer flowing lubricating oil.

The chamber may be provided as a unitary item with the wear adjustmentmechanism, such that removal of the adjustment mechanism from a caliperhousing of the disc brake also results in removal of the chambertherefrom.

Advantageously, the chamber and wear adjustment mechanism togetherdefine a cartridge that can be conveniently removed from the adjustersystem as one item, for maintenance or replacement.

The piston may be hollow, and the chamber may be defined within thepiston.

The structure of the piston provides a convenient way to define thechamber, and reduces the complexity of providing a chamber that inhibitsthe escape of lubricant.

The piston may comprise inner and outer portions, the outer portion maycomprise a cap at an outboard end and a sleeve portion projecting in aninboard direction from the cap, wherein the inner portion and theadjustment mechanism are housed within the sleeve portion of the outerportion.

The cap and inboard projecting sleeve portion of the outer portion ofthe piston define a ‘cup-shape’ that locates the inner portion of thepiston and wear adjustment mechanism and helps to ensure that lubricantfor the adjustment mechanism cannot escape in an outboard directionthrough the outboard end of the outer piston.

The cap and sleeve portion of the outer portion may be integrally andmonolithically formed from the same piece of material.

As the cap and sleeve portion of the outer portion of the piston areintegrally formed, no additional sealing components are required at theoutboard end to prevent loss of lubricant from the chamber in anoutboard direction. Manufacturing costs are also lowered, as only asingle component needs to be produced.

The cap may extend transversely beyond the sleeve and may provide abrake pad support arrangement to distribute the actuating force to thebrake pad.

Advantageously, this arrangement for supporting a brake pad may reduceuneven wear of the brake pad whilst minimizing the number of componentsrequired in the brake.

The cap may further comprise a brake pad mounting arrangement.

Advantageously, the mounting arrangement may act as an anti-rotationfeature for the outer portion and/or as a means for the braking torqueto be transmitted from the brake pad to a carrier of the disc brake.

The chamber may be configured to hold a predetermined amount oflubricant for lubrication of the at least part of the wear adjustmentmechanism in a substantially fluid-tight manner.

Providing a wear adjustment mechanism with a chamber that issubstantially fluid-tight for a given volume of lubrication fluidenables the at least part of the adjustment mechanism to be at leastpartially immersed in a volume of lubricant fluid. This further reduceswear of the components of the adjustment mechanism.

The chamber may comprise an opening at its inboard end, and loss oflubricant in an inboard direction through the opening may be inhibitedby at least one sealing member, which may be located within, orimmediately adjacent, the chamber.

In an adjuster system having this configuration, providing a sealingmember in this location substantially closes one path for lubricant toescape.

The adjuster may further comprise a yoke arranged to actuate the piston,wherein the yoke has an axial bore that accommodates at least a portionof the wear adjustment mechanism. The sealing member may be locatedbetween a surface of the bore of the yoke and an opposing surface of acomponent of the wear adjustment mechanism.

The sealing member closes off a fluid transmission path defined betweenthe bore of the yoke and the wear adjustment mechanism, to help toensure that lubricant from the adjustment mechanism is inhibited fromescaping in an inboard direction.

The wear adjustment mechanism may comprise a drum configured to rotateas part of an adjustment operation. The sealing member may be locatedbetween the surface of the bore of the yoke and an opposing surface ofthe drum.

In a wear adjustment mechanism having this configuration, providing asealing member in this location substantially closes one path forlubricant to escape.

The yoke may have an outboard projecting sleeve portion defining aportion of the axial bore. The sealing member may be located between asurface of the sleeve portion of the yoke and an opposing surface of thepiston.

The sealing member closes off a fluid transmission path defined betweenthe sleeve portion of the yoke and the piston, to help to ensure thatlubricant from the adjuster mechanism is inhibited from escaping in aninboard direction.

The wear adjustment mechanism may comprise an axial bore, and a manualadjuster shaft assembly, for manually retracting the piston extendsthrough the bore, and wherein the sealing member may be located betweena surface of the bore and an opposing surface of the manual adjustershaft assembly.

The sealing member closes off a fluid transmission path, to help toensure that lubricant from the wear adjustment mechanism cannot escapein an inboard direction.

The surfaces may be radially opposing surfaces.

The sealing member may be a lip seal. Alternatively, one or both of theopposing surfaces that locate the sealing member may comprise acircumferential channel, and the sealing member may be an o-ring.

The chamber may comprise an aperture in a radially upper half of thepiston, in the intended installation orientation of the adjuster system,for permitting the passage of air into and out of the chamber.

The aperture allows the chamber to breathe, to allow for extension ofthe piston and temperature changes within the adjuster system, andprevent excessive pressure build-up. As the aperture is in the radiallyupper half of the piston, it helps to prevent fluid loss, assuming adisc brake comprising the adjuster system is not stored upside down.

The aperture may comprise a valve configured to permit air to passthrough the aperture, but prevent fluid from passing through theaperture.

A second aspect of the invention provides a disc brake comprising anadjuster system according to the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 is an isometric view of a brake;

FIG. 2 is a plan view of the brake of FIG. 1, with a brake rotor insitu;

FIG. 3 is an isometric view of the brake of FIG. 1 from an inboarddirection, with the inboard and outboard brake pads omitted for clarity;

FIG. 4 is an isometric view of the brake of FIG. 1 from an inboarddirection, with the outboard brake pad and a caliper housing of thebrake omitted for clarity;

FIG. 5 is an isometric view showing an actuator arrangement of the brakeof FIG. 1, with the inboard brake pad included;

FIG. 6 is a cross-sectional view through an inboard-outboard radialplane 6-6 of the brake of FIG. 1, with no brake pads included;

FIG. 7 is an isometric cross-sectional view through an inboard-outboardhorizontal plane 7-7 of the actuator arrangement of the brake of FIG. 1;

FIG. 8 is a plan view of the isometric cross-sectional view of FIG. 7;

FIG. 9 is a detail cut-away view of an adjustment mechanism of the brakeof FIG. 1, through the plane 9-9 as shown on FIG. 8;

FIG. 10 is an exploded view of the actuator arrangement of the brake ofFIG. 1;

FIG. 11 is a detail view of an outboard end of a manual adjuster shaftof the brake of FIG. 1;

FIG. 12a shows a cross-sectional view through the inboard-outboardhorizontal plane 7-7 of the brake of FIG. 1, but with an alternativemanual adjustment arrangement;

FIG. 12b shows a cross-sectional view through the inboard-outboardradial plane 6-6 of the brake of FIG. 1, but with the alternative manualadjustment arrangement of FIG. 12 a;

FIG. 12c shows a detail view of a manual adjuster shaft of thealternative manual adjustment arrangement of FIG. 12 a;

FIG. 12d shows a cross-sectional view through an end of a manualadjuster shaft, along a plane 12 d-12 d as shown on FIG. 12a , of afurther alternative manual adjustment arrangement of the brake accordingto FIG. 1;

FIG. 13a is a detail view of a spreader plate and the actuatorarrangement of the brake of FIG. 1, with no inboard brake pad included;

FIG. 13b is the same view as FIG. 13a but with the inboard brake padincluded;

FIG. 14 is an isometric view of the spreader plate and carrier of thebrake of FIG. 1, showing how the spreader plate fits within the carrier;

FIG. 15a is an isometric cross-sectional view through theinboard-outboard horizontal plane 7-7 of the brake of FIG. 1, with analternative sealing arrangement according to a further embodiment of thepresent invention;

FIG. 15b shows a plan view of the brake of FIG. 15 a;

FIG. 16 shows a partly schematic view of a portion of the actuatorarrangement of the brake of FIG. 15a , indicating the location ofsealing members within the arrangement;

FIG. 17 shows an isometric view of a cover plate for sealing the housingbore of the caliper of the brake shown in FIG. 15a ; and

FIG. 18 is a cross-sectional view through the inboard-outboard radialplane 6-6 of the brake of FIG. 1, but with a further alternative manualadjustment arrangement.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

Actuation

FIGS. 1, 2 and 3 illustrate a disc brake 2. The disc brake incorporatesan actuating mechanism comprising a single piston suitable for acommercial vehicle. This type of brake is particularly, but notexclusively, suitable for lighter duty heavy vehicles, for examplesmaller trucks, or a trailer of a tractor-trailer combination.

Various orientations of the disc brake are described. In particular thedirections inboard and outboard refer to the typical orientation of thedisc brake when fitted to a vehicle. In this orientation the brake padclosest to the center of the vehicle is the pad directly actuated by anactuation mechanism and being the inboard pad, and the outboard padbeing one mounted to a bridge portion of the caliper. Thus, inboard canbe equated with an actuating side of the disc brake, and outboard with areaction side. The terms radial, circumferential, tangential and chordaldescribe orientations with respect to the brake rotor. The termsvertical and horizontal describe orientations with the disc brakemounted uppermost on an axle, whereas it will be appreciated that in usesuch a disc brake may adopt any axle orientation depending uponpackaging requirements of the vehicle.

The disc brake 2 comprises a caliper 3 having a housing 6 to accommodatethe actuation mechanism and which is slideably mounted on a carrier 4for movement in an inboard-outboard direction.

As can be seen from the view in FIG. 4 with the housing 6 omitted, thecaliper 3 can slide on the carrier 4, by way of first and second guidepins 3 a, 3 b. In this embodiment, the first guide pin 3 a is longerthan the second guide pin 3 b.

An inboard brake pad 11 a comprises a layer of friction material 13 andis arranged so that the friction material 13 faces a brake rotor 10(also known as a brake disc). The inboard pad 11 a is mounted to a brakepad support arrangement. In this embodiment, the inboard brake padsupport arrangement is a spreader plate 60, described in more detailbelow. The inboard pad 11 a is moveable in the direction of arrow 14(see FIG. 2) against the brake rotor 10 (example of rotor shownschematically in FIG. 2).

An outboard pad 11 b, also with a layer of friction material 13, is alsoprovided. The outboard pad 11 b is mounted to a further brake supportarrangement. Suitable means are provided to urge an outboard brake pad11 b against the opposite side of the rotor 10. In this embodiment, suchmeans comprises a bridge 5 arranged so as to straddle the rotor 10 andto transmit the reaction force from an inboard operating shaft 21 to theoutboard pad 11 b. In this embodiment the housing 6 and bridge 5 aremanufactured as a single monolithic casting, but in other embodiments,the bridge 5 may be bolted or otherwise secured to the housing. In thisembodiment, the inboard and outboard brake pads 11 a, 11 b are mountedasymmetrically across an axis parallel to the brake rotor 10. Asdescribed in more detail below, the inboard pad 11 a is mounted in aposition that is laterally offset from the actuation mechanism, i.e.,the line of action of the actuation mechanism does not pass through themid-point of the inboard pad in a circumferential direction. Theoutboard pad 11 b is mounted directly opposite the actuation mechanism,i.e., it is not laterally offset; the line of action of the actuationmechanism does pass through the mid-point of the outboard pad 11 b in acircumferential direction when the outboard pad 11 b is mounted. Thecaliper 3 has an aperture 17, through which the inboard and outboardpads 11 a, 11 b can be inserted and removed in the radial direction.

With reference to the cut-away view of FIG. 5 and cross-section of FIG.6 in particular, the inboard actuation mechanism comprises a singlebrake piston 15 (not shown on FIG. 6 for clarity), slideable in thedirection of arrow 14 (i.e., inboard-outboard) relative to the rotor 10(not shown in FIG. 5, for clarity).

In order to urge the piston assembly in the direction of arrow 14, theoperating shaft 21 is pivoted about rollers 23 which are located along atransverse axis 28. In this embodiment, there are two rollers 23, whichare spaced from one another laterally. Each roller 23 is located on asingle bearing surface 27, each surface 27 being curved to accept theroller 23. Convex surfaces 21 a of the operating shaft 21 are locatedopposite the roller 23. The operating shaft has an axis of rotation 22,being the radial center of the arc defined by the convex surfaces 21 a,which is parallel and offset from the axis 28. The convex surfaces 21 alocate in a semi-circular recess of a yoke 20. A surface 19 of the yoke20 opposite the recess is in contact with an inboard end face of thepiston 15. The operating shaft 21 further comprises a lever 24 having apocket 25 adapted to receive an output push rod (not shown) of a brakeactuator (e.g., an air chamber). The lever 24 is, in this embodiment,shaped as an inverted “U” (see FIGS. 4 and 10 in particular) and theline of action of the brake actuator (from pocket 25) is substantiallyover the line of action of the piston 15.

Located between the convex surfaces 21 a and the recess of the yoke 20,on either arm of the ‘U’ are needle roller bearings 20 a, to enable theoperating shaft 21 to pivot around the roller 23, in the recess of theyoke 20.

In other embodiments, another form of cam surface instead of the convexsurfaces 21 a of the operating shaft 21 may be employed (e.g., a plainbearing) and/or the arrangement may be reversed with the rollers 23being in contact with the yoke 20, and the convex surfaces 21 a beinglocated in the recess of the caliper housing 6.

The yoke 20 further includes a sleeve portion 40, which projects axiallyoutboard from the yoke 20. The yoke 20 has a through bore extendingaxially through its center, the bore also extending through the centerof the sleeve portion 40. In this embodiment, the sleeve portion 40 andyoke 20 are separate components that are fixed together during assembly,in any suitable way, but in alternative embodiments the sleeve portion40 and yoke 20 are integral.

Application of a force in the direction of arrow 26 (FIG. 5) causespivoting movement of the operating shaft 21 about the rollers 23 and theconvex surfaces 21 a bear on the yoke 20. The offset axes 28 and 22cause the yoke 20 to move in the direction of the piston 15, contactingthe piston 15 and causing the piston 15 to urge the friction material 13of the inboard brake pad 11 a directly against the rotor 10. A reactionforce from the operating shaft 21 is transmitted to the bearing surface27 of the caliper 3 via the rollers 23 and is then transmitted to theoutboard pad 11 b via the bridge 5, with the friction material 13 of theoutboard pad 11 b being urged against the rotor 10, such that theinboard and outboard pads 11 a, 11 b clamp the rotor and effect brakingthrough a frictional brake force. In this embodiment, it should be notedthat the piston is not itself directly guided with the caliper. Rather,at the outboard end the position of the piston transverse its line ofaction is determined by interaction of a spreader plate with the brakecarrier as described in more detail below.

Wear Adjustment

A wear adjuster mechanism 30 to maintain a desired running clearancebetween the rotor 10 and inboard and outboard pads 11 a, 11 b isdescribed below. Generally, the operating shaft 21 is connected to aone-way clutch to transfer any rotation of the operating shaft beyond apredetermined degree. Between the one-way clutch and operating shaft area driving link member, which is driven by the operating shaft, and adriven link member which is driven by the driving link member and drivesthe one-way clutch. The one-way clutch has a driving portion configuredto rotate if the driven link member rotates, and a driven portionmounted on the driving portion, that is driven by the portion of theone-way clutch. With particular reference to FIGS. 7, 8, 9 and 10, inthis embodiment the operating shaft 21 includes a sector of a beveldrive gear 33 which extends inwardly from the side thereof parallel tothe axis of rotation 22. The drive gear 33 acts as the driving linkmember and is in driving engagement with a central driven bevel gear 34that acts as the driven link member and is located between the two armsof the operating shaft 21, generally in line with the piston 15. Thebevel gear 34 is in driving engagement with a drive drum 35 that isarranged concentrically with the piston 15 and acts as the drivingportion of the one-way clutch. In other embodiments, a drive pin andslot arrangement may be used instead of the gear arrangement, e.g., apin projecting inwardly from the operating shaft engages a slot that isin driving engagement with the drive drum 35, such that as the operatingshaft pivots in use (function described in more detail below), the pinengages within the slot to cause the drive drum to rotate.Alternatively, the slot may be located on the operating shaft, and a pinmay project outwardly from the drive drum 35, or a component incommunication with the drive drum. In a further alternative arrangement,the pin projects axially inboard from a position offset from the axis ofthe drive drum, rather than inwardly/outwardly.

The drive drum 35 is made up of a collar portion 35 a at its inboard endand an axially extending projecting ‘finger’ portion 35 b, of a smallerdiameter than the collar portion 35 a, that extends outboard from thecollar portion 35 a, concentric with the piston 15. In this embodiment,located adjacent and outboard of the collar portion 35 a of the drivedrum 35, and concentric radially outward from the finger portion 35 b ofthe drive drum 35, is a driven drum 37. The driven drum 37 acts as thedriven portion of the one-way clutch and is mounted on the drive drum35. The driven drum 37 comprises a plurality of axially extendingrecesses 38 which are arranged to accommodate corresponding lugsprojecting radially inwardly from input plates 41 a of a friction clutch41. In other embodiments alternative arrangements for driving the clutchinput plates are contemplated e.g., a different number of recesses, orprojections rather than recesses. A wrap spring 39 is frictionallywrapped around outer circumferential surfaces of the collar portion 35 aof the drive drum 35 and the driven drum 37, such that it bridges thetwo components and enables the two components to act as a one-wayclutch. The wrap spring 39 can easily bridge the two components, as theyare both cylindrical and have the same outer diameter at the locationpoint where the wrap spring 39 engages. In other embodiments othersuitable one-way clutches may be utilized, such as ball and ramp, orroller clutch/sprag clutch arrangements.

The friction clutch 41 comprises output plates 41 b positioned betweenthe input plates 41 a (see FIG. 9 for more detail). The output plates 41b of the clutch 41 have diametrically opposite radially outwardly facinglugs 43, which are not present on the input plates 41 a. Alternatively,a ball and ramp arrangement could be used instead of a friction clutchwith input and output plates, as is known in the art.

The driven drum 37 is retained relative to the drive drum 35 by aretaining ring such as a circlip 36 that is located in a recess in theouter surface of the finger portion 35 b of the drive drum 35, adjacentthe outboard end of the driven drum 37. A stop 44 projects radiallyinwardly from the inner piston 15 b, adjacent and outboard of acircumferential shoulder portion 37 a that projects radially outwardlyfrom the driven drum 37. However, there is a clearance between the stop44 and the shoulder portion 37 a of the driven drum 37. The wrap spring39 is retained in the axially outboard direction by the shoulder portion37 a of the driven drum 37, and in the axially inboard direction by thecollar portion 35 a of the drive drum 35.

As can be seen most clearly from FIGS. 7 and 8, the drive drum 35 isrestrained from moving in an outboard direction by a bush 18. The bush18 is an interference fit with the through bore of the yoke 20 and has aradially inwardly projecting lip at its outboard end, such that anL-shape is defined in cross section. An inboard surface of the lipengages the collar portion 35 a of the drive drum 35, to retain thedrive drum 35 from moving axially outboard, once the brake is assembled.The bush 18 also engages a radially outer surface of the collar portion35 a of the drive drum 35, to restrain the drive drum 35 from movingradially, and to take radial loads that pass from the bevel gear 34through the drive drum 35. There is a clearance between the bush 18 andthe wrap spring 39.

The piston 15 comprises an outer piston 15 a having an internal femalethread, and an inner portion or inner piston 15 b, having acomplimentary external male thread. Therefore, in this embodiment theinner piston 15 b is located within the outer piston 15 a. The innerpiston 15 b has at least one recess in its inner surface. In thisembodiment, the recesses are two longitudinally extending channels 42located diametrically opposite one another. When the adjuster mechanism30 is assembled, the lugs 43 of the output plates 41 b of the clutch 41locate within the channels 42, to key the output plates 41 b to theinner piston 15 b. Therefore, rotation of the output plates 41 b resultsin rotation of the inner piston 15 b.

The components above, that are located between the operating shaft andinner and outer piston, define a transmission path of the wear adjustermechanism 30.

When the adjuster mechanism 30 is assembled, the sleeve portion 40 ofthe yoke 20 is located concentrically between the wrap spring 39 and theinner piston 15 b. The sleeve portion 40 is restrained from rotating, asit is secured to, or integral with, the yoke 20, which is alsoconfigured to be non-rotatable when assembled in the disc brake.However, as described in more detail later, the inner piston 15 b isconfigured to rotate during an adjustment operation, to cause the piston15 to advance in the direction of the inboard brake pad 11 a. A frictionelement is located between the non-rotatable sleeve portion 40 of theyoke 20 and the rotatable inner piston 15 b. The friction element helpsto inhibit undesired vibration-induced torque from affecting theadjustment mechanism in operation, and causing undesired de-adjustmentof the disc brake. Advantageously, the friction element provides aconsistent friction torque but in a small space envelope.

The friction element is preferably configured to resist relativerotation of the yoke 20 and the inner portion 15 b of the piston 15 witha torque greater than the torque required to cause the one-way clutch ofthe adjuster mechanism (in this case the wrap spring 39) to slip whenthe actuation force is released at the end of a braking operation. Thishelps to ensure that the one-way clutch slips rather than permitsunwanted de-adjustment of the brake occurring during brake release.

In this embodiment, the sleeve portion 40 has a circumferential recess40 a on its external surface that is arranged to line up with acorresponding circumferential recess 40 b on the internal surface of theinner piston 15 b, adjacent the inboard end of the inner piston 15 b. Inthis embodiment, the friction element is a radial expander 52, alsoknown as a marcel expander. An example of suitable components may bethose supplied by the Smalley Steel Ring Company of Lake Zurich, Ill.,USA.

The radial expander 52 is located in the annulus defined by theserecesses 40 a, 40 b. The radial expander 52 is a wave formed length ofwire or metal sheet that has been formed into an open ring, which, aswell as producing a radial force to provide resistance to rotation,retains the yoke 20 relative to the inner piston 15 b axially. Morespecifically, the radial expander provides resistance to vibrationinduced torque that can occur during use of the brake, as well ashelping to ensure that movement of the yoke in an axially inboarddirection is transferred to the piston. For example, following a brakingoperation, when the actuation mechanism is reset, axial movement of theyoke results in axial movement of the piston. As the friction elementitself retains the yoke relative to the second portion of the piston,there is no need for extra clips or other components, keeping the numberof parts within the disc brake low. Further, because no additional clipsare needed, manufacturing costs are reduced, as there is no need tomachine the relevant features required for fitting clips to.

In this embodiment, the radial expander 52 is biased in both radialdirections. In other words, the radial expander 52 is configured toexert a force in both a radially inward and a radially outward directionwhen constrained within the annulus, such that it contacts the radiallyoutward facing surface of the recess 40 a of the sleeve portion 40, aswell as the radially inward facing surface of the recess 40 b of theinternal surface of the inner piston 15 b, to provide a force andtherefore a frictional resistance to the relative rotation of the sleeveportion 40 with respect to the radial expander 52 and of the innerpiston 15 b with respect to the radial expander 52. However, the radialexpander 52 could alternatively be rotationally fixed to one of theinner surfaces, and only apply a frictional force to one of thesurfaces. For example, the radial expander 52 could be rotationallyfixed to the sleeve portion 40 and be biased in a radially outwarddirection only, i.e., the radial expander 52 could be configured toexpand only in the direction of the internal surface of the inner piston15 b. In another example, the radial expander 52 could be rotationallyfixed to the internal surface of the inner piston 15 b and be biased ina radially inward direction only, i.e., the radial expander 52 could beconfigured to expand only in the direction of the sleeve portion 40.

To fit the radial expander 52, in this embodiment, the radial expander52 is compressed, e.g., with a mandrel, before being inserted into therecess 40 b of the internal surface of the inner piston 15 b. The innerpiston 15 b would then be slid onto the outboard end of the sleeveportion in an inboard direction, until the radial expander 52 locates inthe annulus defined by the recesses 40 a, 40 b.

In this embodiment, as can be seen most clearly in FIG. 8, the sleeveportion 40 has a chamfer at its outboard end, from the external surfaceof the sleeve portion 40 to the outboard face of the sleeve portion.This chamfer results in the outboard end of the sleeve portion 40 beingtapered in an outboard direction. As the extreme outboard end of thesleeve portion 40 therefore has a smaller outer diameter than theremainder of the sleeve portion 40 that is inboard of the outboard end,fitting of the radial expander 52 is made easier, as the taperedexternal surface at the outboard end acts as a guide surface for fittingthe inner piston 15 b and radial expander 52 onto the sleeve portion 40.

The wear adjuster mechanism 30 additionally comprises a pressure plate45 located outboard and engaging the friction clutch 41. An outboardface of the pressure plate 45 is acted on by a compression spring 47,the compression spring 47 being arranged concentrically between thepressure plate 45 and a washer 48 in order to load the friction clutch41, and generate the required amount of friction to control the torqueat which the friction clutch 41 slips. A retaining ring 49 is providedthat is located in a circumferential recess in the outer surface of thefinger portion 35 b of the drive drum 35, adjacent the outboard end ofthe drive drum 35. The ring 49 is an assembly aid, to help locate theadjustment mechanism during assembly, e.g., at a sub-assembly stage whenall components are not yet installed. The washer 48 is retained by aretaining ring such as a snap ring 50, located concentric with andradially outward of the ring 49, and located in a circumferential recessin the inner surface of the inner piston 15 b. In this embodiment, thesnap ring 50 provides support for the washer 48, to help load thefriction clutch 41. The washer also helps to radially locate the fingerportion 35 b of the drive drum 35.

In this embodiment, the outer piston portion 15 a is integral (i.e.,formed monolithically from the same material by casting, or forging, forexample) with the spreader plate 60. The spreader plate 60 locates theinboard brake pad 11 a, as well as engages surfaces of the carrier 4.Therefore, the interaction of the spreader plate 60 and carrier 4prevent rotation of the outer piston 15 a in use (described in moredetail below).

In order to maintain a desired running clearance between the brake padsand rotor, the wear adjuster mechanism 30 is required to periodicallyadvance the inboard brake pad 11 a towards the rotor 10 to account forthe loss of friction material 13, and to a lesser extent loss ofmaterial from the face of the rotor 10, due to wear.

A predetermined amount of play or backlash is provided in the systembetween the teeth of the drive gear 33 and the teeth of the bevel gear34 (or between the pin and slot, or between the lugs of the input plates41 a of the clutch and the recesses 38, in other arrangements not shownin the figures). In a normal braking operation in which the runningclearance is within the desired parameters, as the operating shaft 21pivots, the play in the system means that no adjustment will occur.

If the running clearance is however greater than the desired range, theaforesaid play is taken up. Whilst there is excess running clearance tobe taken up, this rotation is transmitted via the drive drum 35 to thewrap spring 39, causing the wrap spring 39 to rotate around the drivedrum 35 and driven drum 37 in a direction which causes the wrap spring39 to tighten, transmitting the rotation from the drive drum 35 to thedriven drum 37. More specifically, this rotation is transmitted as thewrap spring bridges the two components, i.e., a first end of the wrapspring 39 engages an outer surface of the drive drum 35 and a second endof the wrap spring 39 engages an outer surface of the driven drum 37.Rotation of the driven drum 37 causes rotation of the input plates 41 aof the friction clutch 41, due to the interaction of the recesses 38 andthe lugs of the input plates 41 a. Rotation of the input plates 41 aresults in rotation of the output plates 41 b, due to the frictionbetween the input and output plates 41 a, 41 b. As the lugs 43 of theoutput plates 41 b engage the channels 42 of the inner piston 15 b, theinner piston 15 b is also caused to rotate.

Since the outer piston 15 a is restrained from rotation by theengagement of the spreader plate 60 and the carrier 4, this causes alengthening of the piston 15 to reduce the running clearance. At thepoint at which the friction material 13 comes into full contact with therotor 10, the torque passing through the adjustment mechanism will startto increase. When this torque increases to a level that is higher thanthe maximum torque value of the friction clutch 41, the friction clutch41 slips and further extension of the piston 15 is prevented. Once thebraking operation ceases, return springs 46 act to urge the operatingshaft 21 back to its rest position. A corresponding retraction of theinner piston 15 b is prevented since the wrap spring 39 relaxes and doesnot transmit a reverse rotation to the driven drum 37.

In this embodiment, the radial expander 52 is configured to resistrelative rotation of the yoke 20 and inner piston 15 b with a torquegreater than the torque required to cause the one-way clutch (in thiscase the wrap spring 39) to slip, when the actuation force is releasedat the end of a braking operation. This helps to ensure that the wrapspring 39 slips rather than permitting unwanted de-adjustment of thebrake occurring during brake release.

The co-axial mounting of the adjuster mechanism 30 within the piston 15minimizes the space required by the mechanism within the housing,resulting in a lighter, more compact housing.

As the wrap spring 39 directly engages the outer surface of the drivedrum 35 and the driven drum 37, any potential backlash that may occurbetween the drive drum 35 and the wrap spring 39, or the driven drum 37and the wrap spring 39, is minimized, which can help to reduce wear ofthe components. Uncontrolled unwinding of the wrap spring 39 is alsominimized, which provides a more predictable, and hence controllable,friction level. The wear on the outer surfaces of the drums 35, 37 isalso minimized. This could, for example, obviate the need to heat treatthese outer surfaces, reducing manufacturing costs. The arrangement alsohelps to remove uncertainties that may arise after manufacturing of thecomponents, for example unpredictable tolerances, which may affect thefunction of the system.

The shoulder portion 37 a on the driven drum 37 and collar portion 35 aof the drive drum 35 limits movement of the wrap spring 39 in theaxially inboard and outboard directions, without the need for furtherseparate circlips, or other similar retaining components.

Manual Rewind Apparatus

Once the friction material 13 has worn to its design limit, it isnecessary for the inboard and outboard brake pads 11 a and 11 b to bereplaced. In order to accommodate the extra depths of unworn new pads ascompared to worn old pads, it is necessary for the piston 15 to berewound back to its retracted position.

To this end, a manual rewind apparatus incorporating an elongate manualrewind shaft 51 is provided (see FIGS. 7, 8 and 10). A hex head 53 orother suitable interface is provided at the outer (user accessible)longitudinal end of the rewind shaft 51. The hex head 53 has a cover 54,which is located on the hex head 53. In this embodiment, the cover 54 isa rubber cap. The cover 54 can be removed by a user when access to thehex head 53 is required. A spanner, wrench or other suitable tool may beattached to the hex head 53 to effect the rewinding operation.

Located outboard of the cover 54, is a collar 56. The collar 56 isgenerally annular and is configured to locate on the rewind shaft 51adjacent the cover 54. The rewind shaft 51 is configured such that itcan freely rotate within the collar 56 e.g., by use of one or more ofsuitable lubrication, coatings such as PTFE, or by the collarincorporating a lip seal that minimizes the contact areas between thecollar and shaft. In this embodiment, the collar 56 includes acircumferential recess 56 a facing inboard. Within the recess 56 a arefirst and second sealing members 56 b and 56 c. In this embodiment, thefirst sealing member 56 b is generally cup shaped, with a base having acentral aperture, and sides projecting inboard, to define a generalL-shape in cross-section on each side. The base of the sealing memberengages with the collar 56 to substantially seal lubricant within thehousing 6 of the brake and help prevent foreign material fromcontaminating the housing 6 of the brake. In this embodiment, the secondsealing member 56 c is a spring energized sealing ring that engages aslot in an internal surface of the recess 56 a of the collar 56, tofurther help seal lubricant within the housing 6 of the brake, and helpprevent foreign material from contaminating the housing 6 of the brake.

When the brake is assembled, the rewind shaft 51, collar 56, and cover54 are located within a through bore, extending from an inboard surfaceof the caliper 3. The cover 54 is retained within the housing with aretaining member 54 b, which locates within a circumferential slot onthe external surface of the cover 54, between the cover 54 and the boreof the caliper 3. In this embodiment, the retaining member 54 b is anannular retainer with an inner surface that engages the outer surface ofthe cover 54, and circumferential protrusion projecting radiallyinwardly and engaging the slot. Preferably, the retaining member 54 b ismetal.

The rewind shaft 51 is mounted concentrically and radially inwardly withrespect to the components of the adjustment mechanism 30. At theoutboard end longitudinally opposite the hex head 53, a piston engagingend piece 55 is mounted on the rewind shaft 51. In this embodiment, theend piece 55 is circular in profile, with two diametrically opposedprojections 57. As can be seen from FIG. 11, the end piece 55 and theprojections 57 are dimensioned such that the projections 57 locatewithin the channels 42 of the inner piston 15 b. The channels 42 allowthe inner piston 15 b to advance during a braking operation, whilst therewind shaft 51 is axially fixed.

In use during manual adjustment therefore, a user rotates the hex head53 to rotate the rewind shaft 51. Due to the engagement between theprojections 57 of the end piece 55 and the channels of the inner piston15 b, the inner piston 15 b is caused to rotate, rewinding the piston 15back to its original retracted position.

Torque Limiting Arrangement

An alternative rewind mechanism arrangement is shown in FIGS. 12A, 12Band 12C. Like parts are labelled by like numerals in FIGS. 12A to 12C bycomparison with FIGS. 1-12. Parts that differ from FIGS. 1-12 have thesuffix ′.

When the adjuster mechanism is fully de-adjusted, the inner piston will‘bottom out’ on the combined spreader plate and outer piston. In thisembodiment, it can be seen in FIG. 8, that the outboard end surface ofthe inner piston 15 b will engage an inboard surface of the spreaderplate 60 when the adjuster mechanism is fully de-adjusted. Once this hashappened, any further de-adjustment, e.g., by an impact wrench, canseriously damage the internal components of the adjuster mechanism.

Therefore, in the arrangement of FIGS. 12A, 12B and 12C, an alternativeend piece arrangement is provided to act as an overload device. In thisarrangement, the inboard longitudinal end has a diametric slit 55 a′ inits inboard surface. The slit 55 a′ has a sufficient depth relative tothe inboard surface that it can house a strip 55′. In this embodiment,the strip 55′ is generally rectangular in shape, with a length such thatwhen the adjuster mechanism is assembled, longitudinal ends 57′ of thestrip 55′ locate within the channels 42 of the inner piston 15 b.Advantageously, the strip and slit arrangement is cheap to manufactureand easy to assemble.

As in the arrangement of FIGS. 7, 8, 10 and 11, in use, a user rotatesthe hex head 53 to rotate the rewind shaft 51. Due to the engagementbetween the longitudinal ends 57′ of the strip 55′ and the channels 42of the inner piston 15 b, the inner piston 15 b is caused to rotate,rewinding the piston 15 back to its original retracted position.

However, in the arrangement of FIGS. 12a, 12b and 12c , the strip 55′also acts as a torque limiting arrangement, to prevent damage to theadjuster mechanism 30 if too high a torque is applied to the hex head53.

The strip 55′ is made of a deformable material such that, if a torque isapplied to the hex head at a torque level in excess of the maximumdesired torque level of the system, the strip 55′ will deform,disengaging the longitudinal ends 57′ from the channels 42. Therefore,rotation of the rewind shaft 51 will not be transmitted to the innerpiston 15 b, and no damage will be caused to the inner piston 15 b, orother components of the adjuster mechanism, by the excessive torqueapplied. In preferred embodiments, the deformation is elastic, such thatthe strip can be considered an elastically deformable member and willreturn to its original shape when back in alignment with the channels42.

After rotation of the rewind shaft 51 by 180 degrees, the longitudinalends 57′ will again drivingly engage the channels 42, so rewinding ofthe pads can continue. However, if the torque being applied is still toohigh, the strip 55′ will again deform, and the rotation of the rewindshaft 51 will not be transmitted to the inner piston 15 b. Thelongitudinal ends 57′ will not drivingly engage the channels 42 untilthe torque being applied to the rewind shaft 51 is below the desiredlevel, at which point the torque will be transmitted from the rewindshaft 51 to the inner piston 15 b, to rewind the piston 15 and increasethe clearance between the rotor 10 and the inboard pad 11 a.

In this embodiment, the strip 55′ is spring steel, but it will beappreciated that any suitably elastic material could be used. Also, inthis embodiment, the strip 55′ and slit 55 a′ are fixed to one anotherby way of a push fit arrangement, but it will be appreciated thatalternative arrangements could perform the same function. For example,the strip 55′ could be wrapped around the rewind shaft 51, welded to therewind shaft 51, attached to the rewind shaft 51 by an adhesive, rivetedto the rewind shaft 51, peened, pressed, formed, or any other suitablemethod used. The rewind shaft 51 and the strip 55′ could be integral.The slit 55 a′ may not be necessary if one of these alternativearrangements are used.

Alternatively, instead of a strip and shaft arrangement, the end piece55 could be a gear, and the projections 57 of the end piece 55 could begear teeth that engage in corresponding recesses in the inner piston 15b. The teeth could be arranged to deform at a predetermined load, i.e.,if a torque is applied to the hex head at a torque level in excess ofthe maximum desired torque level of the system. In a differentembodiment, the gear itself could be configured to withdraw the gearteeth radially in at a predetermined load, for example by being like agovernor and having linkages that bring the gear teeth in.

In a further alternative, the end piece 55 could be a shallow cone witha circumferential rim having projections 57 that engage with the innerpiston 15 b. If a torque is applied to the hex head at a torque level inexcess of the maximum desired torque level of the system, the cone coulddeform elastically to define a sharper angle and prevent the projections57 from driving the inner piston 15 b.

In this embodiment, the strip 55′ is a planar rectangular shape. Afurther alternative arrangement, however, is shown in the schematiccross-sectional view of FIG. 12D. Parts that differ from FIGS. 12A to12C have the suffix ″.

In FIG. 12D, the strip 55″ has angled longitudinal ends. The strip 55″is shaped such that a central portion locates within the slit 55 a″ ofthe rewind shaft 51″, but the longitudinal ends 57″, which are eitherside, axially, of the central portion, are angled away from the centralportion. The longitudinal ends are angled relative to a transverse axisT-T that passes through the center of the rewind shaft. The longitudinalends are angled to the axis T-T by an angle α. Preferably, the angle αis 0 to 60 degrees. Even more preferably, the angle α is 3 to 40degrees. In this embodiment, the longitudinal ends are angled in anangular direction opposite the angular direction R, which is the samedirection that the rewind shaft 51″ is rotated during a rewindoperation. This angled arrangement biases the torque such that the strip55″ slips at a lower torque in the rewind direction than in theadjustment direction. This helps to ensure that, for example, if thepiston 15 is located at the end of its travel, i.e., it is fullyrewound, the natural friction within the system will not cause the strip55″ to slip if the piston 15 is adjusted manually to close the rotor gapagain after a pad replacement operation. The angle is chosen such thatthere is a sufficient angle for the strip to engage the channels 42 ofthe inner piston. If the angle is too great, then the strip will notengage with the channels 42 of the inner piston as they would just slipout as the shaft is rotated.

Alternatively, instead of a constant angle α, the angle could vary. Inone embodiment, the angle could vary such that the strip is curved,e.g., to define an ‘S-shape’, in cross section, when looking from theoutboard direction. In this case, adjusting would only be possible inone direction.

A further advantage of either the angled or curved arrangements is thatstrength in one direction is increased, which enables the strip to bemade from thinner or cheaper material.

Mounting of Brake Pads

FIGS. 13A and 13B show the spreader plate 60 that is located on theinboard side of the rotor 10, the spreader plate 60 being shown bothwith and without an inboard brake pad 11 a. As will be described, inuse, the spreader plate 60 is configured to be guided by the carrier 4.For clarity, the carrier 4 is not shown in FIGS. 13A and 13B. The mainfunction of the spreader plate 60 is to spread the load applied by thesingle piston across the circumferential width of the inboard pad 11 a,which is particularly useful for high pressure applications (e.g.,stopping a vehicle at high speed), to more evenly distribute the loadapplied to the pads, and help prevent brake fade. There is also aneffect on wear; i.e., wear closer to the center of the pad (where thepiston is applied) can be reduced, to provide a more even distributionof wear.

As can be seen most clearly in FIG. 14, the carrier 4 has a spreaderplate opening 70, for locating the spreader plate 60. The opening 70 isarranged to support the spreader plate 60 in a circumferential(rotational about an axis passing through the center of the rotor andpads) direction, i.e., to provide a reaction force that reacts thecircumferential forces created within the brake when the piston isactuated and the pads clamp the rotor.

Within the opening 70, the carrier 4 has opposing vertical spreaderplate abutment surfaces 72, located on ‘arms’ that project radiallyoutward from the left and right sides of the carrier 4 (the ‘left’ and‘right’ directions being relative to the hub of a wheel, when thecarrier 4 is mounted in use).

The carrier 4 also has horizontal spreader plate abutment surfaces 74,located either side of an arched ‘link’ portion 4 a of the carrier, thelink portion 4 a connecting the left and right sides of the carrier 4.

When the brake is assembled, the vertical abutment surfaces 72 contactvertical outer side surfaces 62 of the spreader plate 60, and thehorizontal abutment surfaces 74 contact horizontal bottom surfaces 64 ofthe spreader plate 60. This arrangement restrains rotation of thespreader plate 60. As the spreader plate 60 and the outer piston 15 aare, in this embodiment, a single integral component, then the rotationof the outer piston 15 a is also restrained. Therefore, when the brakeis actuated in use, and when the brake is adjusted, the spreader plate60 and outer piston 15 b are restrained from rotating.

The spreader plate 60 has two side steps 65 projecting axially outboardfrom the outboard surface of the spreader plate 60. Each side step 65extends down a vertical side edge of the spreader plate and across partof the horizontal bottom edge of the spreader plate 60, to definevertical pad abutment surfaces 66 and horizontal pad abutment surfaces68.

Preferably, the vertical pad abutment surfaces 66 and horizontal padabutment surfaces 68 are machined, but they could be forged, or justleft as cast as desired. Typically, there is a tolerance of about 0.5mm. Machining the surfaces enables them to be used as a datum duringmanufacturing.

The vertical and horizontal pad abutment surfaces 66, 68 define a firstpad mounting structure in the form of an opening 69 that is arranged tosupport the pad in a radially inward and circumferential (i.e.,rotational) direction. As the brake is actuated, the abutment surfaces66, 68 react the torque that is created as the inboard pad 11 a clampsthe rotor 10. The abutment surfaces 66, 68 also act to locate theinboard brake pad 11 a.

Advantageously, as the forces from the inboard pad 11 a are reacted bythe side steps 65, and these forces then passed directly to the abutmentsurfaces 72, 74 of the carrier 4, the backplate of the inboard pad canbe made significantly thinner than the backplate of brake pads in brakesof the prior art. For example, a typical backplate may have a thicknessof 7 to 10 mm, whereas a backplate used in combination with the spreaderplate 60 could have a thickness of 5 mm, or even lower. It will be clearthat the potential of being able to use thinner brake pad backplateswould result in cost savings during manufacture of the pads andpotentially an overall weight saving in the brake. Further weight/costsavings could be made by optimizing the brake support arrangements. Forexample, cut outs could be provided in areas of the spreader plate orcaliper where forces in use will be lower, to save weight. Thearrangement may also reduce the risk of relatively thin backplates andor carrier abutment surfaces being damaged due to impact loads etc. fromvibrations and brake torque loads. Finally, the spreader platearrangement for retaining the backplates means that, even for very thinbackplates, the risk that a brake pad will fall through the gap betweenthe spreader plate and the rotor (e.g., when the friction materialand/or the rotor is heavily worn) is very low. This is a significantsafety improvement.

Further, in other embodiments the backplate may be provided withalternative or additional formations to transmit the braking torqueloads to the spreader plate 60, so that, provided the spreader plateprojects beyond the edges of the inboard pad 11 a the spreader platetransmits the load to the carrier. These formations may comprise forexample projections from the rear face of the backplate intocorresponding recesses of the spreader plate, or vice versa.

Further, instead of vertical and horizontal abutment surfaces, thesurfaces may instead be angled to some degree, e.g., the radiallyoutermost spacing between the generally vertical surfaces may be widerthan the radially innermost spacing so a trapezoidal shape is formed.Further, the surfaces may be curved, e.g., so that the horizontal andvertical surfaces merge.

Sealing of Housing

To seal the adjustment mechanism 30 within the housing 6 of the caliper3, a cover plate 75 seals the outboard opening of the housing 6. Thecover plate 75 has a central bore 76, which the piston 15 passesthrough.

As shown most clearly in FIGS. 7, 8 and 10, a sealing boot 76 a islocated on the piston 15, outboard of the cover plate 75. The sealingboot 76 a is convoluted and creates a seal between the bore 76 of thecover plate 75 and the outer surface of the outer piston 15 a.

A circumferential seal 77 is provided between the cover plate 75 and theoutboard opening in the caliper 3. The seal 77 generally follows theouter profile of the cover plate 75 and acts against the outboardsurface of the housing 6 of the caliper and the cover plate 75 toinhibit contaminants passing through the space between the cover plate75 and the caliper 3.

A secondary convoluted seal 78 is located inboard of the boot 76 a, tofurther inhibit contaminants passing between the outer piston 15 a andthe cover plate 75, in the event that the primary seal fails. Thecircular profile of the piston and sealing arrangement means thateffective sealing can be achieved without complex sealing arrangements.Alternatively however, other profiles of the piston and sealingarrangement can be used and still achieve effective sealing. Forexample, an elliptical profile could be used, or a substantially lobularprofile.

The cover plate 75 has two half-spherical protrusions 79 projecting fromits inboard surface. As can be seen from particularly FIG. 8, theseprotrusions 79 act as a seat for the outboard ends of the two returnsprings 46. The inboard ends of the return springs 46 are seated onoutboard extending protrusions of the yoke 20, such that when a brakingoperation has ceased, the operating shaft 21 is pushed back to its restposition. In an alternative arrangement, a single seal could be providedon the outer surface of the piston, to act between the outer surface ofthe piston and an inner surface of the cover plate. Preferably, the sealwould project in a radially outward direction.

A spring clip 81 is shown in FIG. 10, which retains the cover plate inan outboard direction in a mouth of the housing 6 of the caliper 3.Alternatively, axial bolts, or other suitable fixing components, couldbe used (not shown). If a spring clip is used, the cover plate would beprevented from moving too far in the inboard direction by the steppedarrangement to the mouth.

Alternatively, a radially-directed seal could be provided on the coverplate, as shown in FIG. 17. In this embodiment, an alternative coverplate 75′ is provided. The cover plate has a flange portion 75 a′ thatis substantially parallel to the orientation of the brake pads and facesof the rotor for engaging the outboard face of the housing 6 to limitmovement inboard, and a portion 75 b′ projecting inboard from theflange, such that the portion 75 b′ projects through the opening in thehousing 6 and locates within the cavity of the housing 6 of the caliper3 and defines a radially outer surface that is normal to the plane ofthe flange portion and is substantially parallel to the inboard-outboardaxis.

In this embodiment, the flange portion 75 a′ of the cover plate 75′ hasfirst and second lateral lugs 75 c′, which are configured to engage theoutboard face of the housing 6 of the caliper 3. Each lug 75 c′ has asingle aperture 75 d′ for locating a fastening member (not shown), suchas a bolt or a rivet, to fasten the cover plate 75′ to the outboard faceof the housing 6 of the caliper 3. Therefore, the cover plate 75′ isfastened to the outboard face of the housing 6 only at the lateral lugs75 c′, to retain the cover plate 75′ relative to the housing 6 in anoutboard direction. In other words, the apertures are locatedcircumferentially either side of the cover plate, so that the fasteningmembers can be located in the outboard face of the housing portioncircumferentially either side of the mouth of the housing cavity, toretain the cover plate relative to the housing portion in an outboarddirection.

As only two fastening members are required to fasten the cover plate tothe housing portion, assembly is simplified, as the location of the twofastening members means that they are easier to access, there are fewerfastening operations required, and less machining overall is necessary,all contributing to a reduced cost of manufacture.

First and second sealing elements 77′ are located between the radiallyouter surface of the cover plate portion 75 b′ and the radially innersurface of the mouth of the cavity of the housing 6 of the caliper 3.The radially outer surface of the cover plate portion 75 b′ and theradially inner surface of the cavity of the housing 6 oppose oneanother. The sealing elements 77′ inhibit contamination of the housingcavity. As the sealing elements 77′ act between opposing surfaces of thecavity of the housing 6 and the cover plate portion 75 b′, the integrityof the seal is less affected by deformations of the outboard end of thehousing cavity that can occur during the life of the disc brake.Further, the seal does not require a clamp loading generated by thefasteners to seal effectively. Therefore, environmental exposure isminimized, and the risk of failure and subsequent contamination of thehousing cavity is reduced compared to arranging a gasket between theoutboard face of the housing and a cover plate, as is normal in priorart sealing arrangements. Manufacturing costs may also be lowered, asthe sealing faces may be in the same orientation as other internal facesof the housing cavity that require machining (such as guide surfaces ofthe yoke or operating shaft), so an additional machining operation tocut the sealing faces may not be required to be in an oppositedirection, which would otherwise increase costs.

In an alternative embodiment (not shown), the cavity of the housing 6tapers radially inwardly from the outboard face of the housing 6 in aninboard direction, and the portion 75 b′ of the cover plate 75′ locatedwithin the cavity of the housing 6 tapers radially inwardly in aninboard direction. The tapered cavity of the housing 6 and tapered coverplate portion 75 b′ may help to increase the integrity of the seal asthe fasteners may be used to apply a pre-load to the sealing interface,as well as help to self-center the cover plate portion within thehousing cavity, to create an equal clearance around the entirecircumference of the cover plate portion, and therefore a moreconsistent seal. In an alternative embodiment, only the cover plateportion 75 b′ is tapered, to create a seal with a non-tapered housingcavity. The angle of the taper may be in a range of 0° to 45° withrespect to the fitting direction, preferably 0°-30°.

Each sealing element 77′ can be mounted on the radially outer surface ofthe cover plate portion 75 b′. In this embodiment, the radially outersurface of the cover plate portion 75 b′ has a first circumferential anda second circumferential recess. In this embodiment, the correspondingradially inner surface of the mouth of the housing has a straightprofile inboard-outboard. In other embodiments, the radially innersurface of the mouth of the housing 6 may alternatively be provided withcorresponding first and second circumferential recesses. In other words,the first recess of the cover plate portion 75 b′ may line up with thefirst recess of the cavity of the housing 6 and the second recess of thecover plate portion 75 b′ may line up with the second recess of thecavity of the housing 6, to define channels for locating the first andsecond sealing elements 77′.

Each sealing element is resilient such that, given an appropriatedimensioning of the seal in a relaxed state relative to the mouth of thecavity, the sealing element comes into contact with the radially innersurface of the mouth of the cavity, to create a seal.

The cover plate may be metallic, a composite, a high-temperaturepolymer, or any other suitable material. The cover plate could besuitable for being manufactured by casting, pressing, injection molding,or any other suitable process. In one embodiment the cover plate may bemanufactured from sheet metal of a thickness of around 1 mm to around 3mm.

In this embodiment, each sealing element 77′ is a resilient sealingelement, such as an o-ring. The o-ring may have a cross-sectionaldiameter of around 5 mm, which is reduced to 2-3 mm when the o-ring isunder tension (due to being stretched around the cover plate portion 75b′) and compression (from contact with the radially inner surface of themouth of the cavity), when located between the cover plate and housingcavity. The clearance between the cover plate portion and the housingcavity should typically be between a loose running fit and a closerunning fit in accordance with ISO standards. E.g., for a close runningfit the clearance may be approximately 0.1-0.2 mm.

In other embodiments though, each sealing element could be an extrudedseal, an energized gasket with a metallic frame, or an over-moldedsealing element. In the case of an extruded seal, in some embodiments,the cover plate may be fitted to the housing whilst the seal is “wet”and uncured, such that curing occurs in situ.

If the sealing element is resilient, an outer perimeter of the sealingelement may be greater than the circumference of the radially innersurface of the housing cavity. In this case, the sealing element must becompressed to install the cover plate in the housing, helping to ensurethat there is contact between the inner surface of the housing cavityand the sealing element, to increase the reliability of the seal.

The cover plate further includes a pair of integral radially upwardprojecting fingers 93, to define a radially upward facing depression,for locating the pad retaining strap 92. The depression helps to ensurethat the pad retaining strap 92 is restrained in the circumferentialdirection, without a separate component being required. As best seen inFIG. 2, a bolt 94 (or other appropriate fastening component) passesthrough the pad retaining strap 92 and into a threaded bore in thecarrier 4, to releasably secure the pad retaining strap 92 in place.

The bore 76 of the cover plate 75′ could also be configured for guidinga supporting the piston 15 of the disc brake. Preferably, the clearancebetween the piston 15 and the bore 76 of the cover plate 75′ is suchthat the piston 15 can freely actuate within the bore 76, without anyguiding from the cover plate in normal operation but restrain radialmovement of the piston when during storage and installation on avehicle. In other embodiments the cover plate may be used to support andguide the piston 15 in normal operation, in particular in a radialdirection. In one embodiment, the piston could have a bush, such as anylon bush, to help ensure the piston is guided by and free to actuatewithin the bore.

In alternative embodiments, the seal may be fitted to the radially innerface of the mouth, rather than the cover plate, and the number of sealsmay be increased or decreased as required. Whilst the use of only twomounting apertures and corresponding fasteners is described, in otherembodiments a different number of apertures and fasteners may beprovided, and in different locations. The cover plate may be providedwith two or more bores therein to receive two or more actuating pistons.

Adjuster Sealing

As described above, the components of the adjuster mechanism 30 arecontained within the piston 15, i.e., a chamber 120 is definedconcentrically within the inner piston 15 b and the outer piston 15 a,for locating the adjuster mechanism 30.

Looking now at FIGS. 15A and 15B, an arrangement is provided forsubstantially sealing the chamber 120. The chamber 120 is substantiallyfluid-tight, so as to hold oil, or other suitable lubricating fluid forlubrication of the adjuster mechanism.

At the outboard end, the inboard surface of the spreader plate 60 andthe radially inner surface of the outer piston 15 a define an inboardfacing ‘cup-shape’ that locates the inner portion of the piston andadjuster mechanism and helps to ensure that lubricating fluid from theadjuster mechanism cannot escape in an outboard direction through theoutboard end of the outer piston. In this embodiment, the cap and sleeveportion of the outer portion of the piston are integrally formed.

In embodiments where the spreader plate 60 and the outer piston 15 a areintegrally formed, no additional sealing components are required at theoutboard end to prevent loss of lubricating fluid from the chamber 120in an outboard direction.

The chamber 120 comprises an opening at its inboard end, and loss oflubricating fluid in an inboard direction through the opening isinhibited by at least one separate sealing member, which is locatedwithin, or immediately adjacent, the chamber. In this embodiment, afirst sealing member 121, a second sealing member 122 and a thirdsealing member 123 are provided. The first sealing member 121 is locatedon the rewind shaft 51, between the rewind shaft 51 and the outboard endof the finger portion 35 b of the drive drum 35. The second sealingmember 122 is located on an outer surface of the sleeve portion 40 ofthe yoke 20, between the outer surface of the sleeve portion 40 and theinner piston 15 b. The third sealing member 123 is located on the collarportion 35 a of the drive drum 35, between the collar portion 35 a andan inner surface of the through bore of the yoke 20. Suitablecircumferential grooves would be provided in the components discussedabove, to locate the sealing members.

Therefore, in use, a ‘bath’ of lubricating fluid is retained within thechamber 120, i.e., substantially no lubricant can pass inboard of thefirst sealing member 121 and out through a potential fluid transmissionpath defined between the drive drum 35 and the rewind shaft 51, orinboard of the third sealing member 123, through a potential fluidtransmission path defined between the yoke 20 and the drive drum 35. Theadjuster mechanism can be at least partially submerged in the ‘bath’ ofthe lubricating fluid. This reduces wear of the components of theadjuster mechanism, extending the life of a disc brake comprising thisadjuster system.

In this embodiment, the first, second and third sealing members 121,122, 123 are elastomeric o-rings, but it will be appreciated that anysuitable sealing members could be used with minor modifications to thesealing arrangement that would be within the remit of the skilledperson, e.g., lip seals, u-cups, metal sealing discs, etc.

The chamber 120 is preferably not be completely air-tight, as pressurevariations can occur due to extension of the piston 15 during adjustmentand temperature changes within the brake in use. Therefore, an aperturesuch as a breather hole 124 is provided that passes from an outersurface of the outer piston 15 a to an inner surface of the outer piston15 a. A possible location for the breather hole 124 is shownschematically in FIG. 16. The location is chosen such that there will beminimal loss of lubricant out of the breather hole 124. As the outerpiston 15 a does not rotate during use, a breather hole 124 in aradially upper half of the outer piston 15 a is preferable. It ispreferable that lubricating fluid be filled to a level radially lowerthan the location of the breather hole 124, to help prevent fluid loss.Lubricant loss would only occur if the brake, or vehicle the brake isattached to, is stored upside down, which is unlikely to occur. Tofurther help prevent lubricant loss, a valve which is configured topermit air to pass but prevent fluid, e.g., a bung or similar, could belocated in the breather hole 124.

In alternative arrangements, the chamber 120 is not fluid-tight, butsimply configured to contain lubricant for lubrication of at least partof the wear adjustment mechanism, and inhibit lubricant from migratingaway from the wear adjustment mechanism. As the lubricant is inhibitedfrom escaping from a defined location, it is restricted from migratingto other areas of the disc brake 2, reducing wear of the components ofthe adjustment mechanism, and extending the life of a disc brake 2comprising this adjuster system. If the lubricant is grease or alubricating oil, a higher quantity of lubricant can be maintained nearthe parts of the wear adjustment mechanism needing lubrication, such asthe wrap spring and/or friction clutch plates. Thus, should there be adegradation or escape of the lubricant over time, a greater amount oflubricant will nevertheless remain in contact with the parts requiringlubrication.

One way to inhibit the lubricant is for the chamber and/or the wearadjustment mechanism to have a radial step arranged to define a barrierto inhibit the escape of lubricant in an inboard or outboard direction.For example, looking at FIGS. 7 and 8, the stop 44 of the inner piston15 b projects radially inwardly and is arranged in an inboard directionby the compression spring 47, such that it will engage the outboard faceof the shoulder portion 37 a of the driven drum 37. Therefore, anylubricant contained outboard of the stop 44 will be inhibited fromescaping in an inboard direction past the stop. The pressure plate 45could also be dimensioned to extend radially to a sufficient extent tooverlap and perform the same function, i.e., inhibit lubricant fromescaping.

As a disc brake is mounted in a fixed orientation on a vehicle,provision of a radial step tends to inhibit the escape of at least aportion of lubricant under gravity and may help to create a moretortuous path out of the chamber for lubricant in the event of lubricantbeing dislodged by virtue of the disc brake being subjected tovibration, jolts or the like. The radial step may advantageously extendaround a complete circumference, such that a barrier exists irrespectiveof the orientation of the disc brake on a vehicle.

The chamber and/or the wear adjustment mechanism may also have first andsecond opposed interface surfaces having a spacing sufficiently smalltherebetween so as to act a barrier to inhibit the escape of lubricantin an inboard or outboard direction. As an example, the pressure plate45 or the circlip 36 could be dimensioned to extend radially asufficient extent to define only a small radial spacing between the twocomponents, to inhibit lubricant from escaping. Alternatively, thesleeve portion 40 of the yoke 20 could extend further in the outboarddirection, such that its radially inner surface opposes the radiallyouter surface of the shoulder portion 37 a of the driven drum 37.

First and second opposed interface surfaces further improve thecontainment of lubricant within the chamber. The surfaces may beradially opposed or axially opposed. The spacing required may be largerfor relatively viscous lubricants such as grease, and a closer fit forthinner.

The chamber 120 may be provided as a unitary item with the wearadjustment mechanism, such that removal of the adjustment mechanism fromthe caliper housing 6 of the disc brake 2 also results in removal of thechamber therefrom, for maintenance or replacement.

FIG. 18 shows an alternative adjuster mechanism 230, which also enablesa simple arrangement to be provided, for substantially sealing a chamber270.

The components of the adjuster mechanism 230 are contained within apiston 215, i.e., the chamber 270 is defined concentrically within aninner piston 215 b and an outer piston (not shown in FIG. 18), forlocating the adjuster mechanism 230.

This actuation mechanism arrangement enables a simple arrangement to beprovided for substantially sealing the chamber 270. The chamber 270 issubstantially fluid-tight, so as to hold oil, or other suitablelubricating fluid for lubrication of the adjuster mechanism.

At the outboard end, a sealing member can be provided at location 272,to act between a stop 249 and a radially inner surface of the innerpiston 215 b. Alternatively, a sealing member can be provided atlocation 274, to act between a second washer 245 b and the radiallyinner surface of the inner piston 215 b. In one embodiment the sealingmember at location 272 or 274 may be shaped so as to extend into andsubstantially close off the channels 242, or the channels may be closedoff by separate components from the seal (not shown).

This outboard sealing arrangement helps to ensure that lubricating fluidfrom the adjuster mechanism is inhibited in an outboard directionthrough the outboard end of the outer piston. The outboard sealingarrangement acts in combination with a spreader plate and the outerpiston (both not shown in FIG. 18 for clarity), which are integrallyformed, also helping to prevent loss of lubricating fluid from thechamber 270 in an outboard direction.

In some embodiments (not shown in FIG. 18), a central axial manualrewind apparatus incorporating an elongate manual rewind shaft isprovided, to rewind the piston 215 back to its retracted position whenit is necessary for the brake pads to be replaced, for example. In oneexample of a manual rewind apparatus, a piston engaging end piece ismounted on the manual rewind shaft. The end piece can be generallycircular in profile, but with two diametrically opposed projections. Theend piece and the projections are dimensioned such that the projectionslocate within longitudinally extending channels of the inner piston 215b. The channels allow the inner piston 215 b to advance during a brakingoperation, whilst the shaft is axially fixed.

In use during manual adjustment, therefore, a user rotates the rewindshaft. Due to the engagement between the projections of the end pieceand the channels of the inner piston 215 b, the inner piston 215 b iscaused to rotate, rewinding the piston 215 back to its originalretracted position.

The chamber 270 comprises an opening at its inboard end, and loss oflubricating fluid in an inboard direction through the opening can beinhibited by a further sealing arrangement located at the inboard endwithin, or immediately adjacent, the chamber 270. In this embodiment, asealing member can be provided at location 276, between anoutboard-facing surface of a bearing 218 a and an inboard-facing surfaceof a shoulder 240 a of a sleeve portion 240 of a yoke 220. A sealingmember can also be provided at location 278, between a radially outersurface of a collar 235 c of a drive drum 235 and a radially innersurface of the yoke 220.

Therefore, in use, a ‘bath’ of lubricating fluid is retained within thechamber 270, i.e., substantially no lubricant can pass inboard of theinboard sealing arrangement through a potential fluid transmission pathdefined between the yoke 220 and the drive drum 235. Similarly, nosubstantially no lubricant can pass outboard of the outboard sealingarrangement through a potential fluid transmission path defined betweenthe inner piston 215 b and the adjuster mechanism 230. The adjustermechanism can be at least partially submerged in the ‘bath’ of thelubricating fluid. This reduces wear of the components of the adjustermechanism, extending the life of a disc brake comprising this adjustersystem.

The sealing members are preferably elastomeric o-rings, but it will beappreciated that any suitable sealing members could be used with minormodifications to the sealing arrangement that would be within the remitof the skilled person, e.g., lip seals, u-cups, metal sealing discs,etc.

In alternative arrangements, the chamber 270 is not fluid-tight, butsimply configured to contain lubricant for lubrication of at least partof the wear adjustment mechanism, and inhibit lubricant from migratingaway from the wear adjustment mechanism. As the lubricant is inhibitedfrom escaping from a defined location, it is restricted from migratingto other areas of the disc brake, reducing wear of the components of theadjustment mechanism 230, and extending the life of a disc brake 202comprising this adjuster mechanism 230. If the lubricant is grease or alubricating oil, a higher quantity of lubricant can be maintained nearthe parts of the wear adjustment mechanism needing lubrication, such asthe wrap spring and/or friction clutch plates. Thus, should there be adegradation or escape of the lubricant over time, a greater amount oflubricant will nevertheless remain in contact with the parts requiringlubrication.

One way to inhibit the lubricant is for the chamber and/or the wearadjustment mechanism to have a radial step arranged to define a barrierto inhibit the escape of lubricant in an inboard or outboard direction.For example, looking at FIG. 18, the stop 244 of the inner piston 215 b,which projects radially inwardly could be dimensioned and arranged toinhibit any lubricant contained outboard of the stop 244 from escapingin an inboard direction past the stop 244. The first washer 245 a couldalso be dimensioned to extend radially to a sufficient extent to overlapand perform the same function, i.e., inhibit lubricant from escaping.

As a disc brake is mounted in a fixed orientation on a vehicle,provision of a radial step tends to inhibit the escape of at least aportion of lubricant under gravity and may help to create a moretortuous path out of the chamber for lubricant in the event of lubricantbeing dislodged by virtue of the disc brake being subjected tovibration, jolts or the like. The radial step may advantageously extendaround a complete circumference, such that a barrier exists irrespectiveof the orientation of the disc brake on a vehicle and the angularposition of the inner piston 215 b.

The chamber and/or the wear adjustment mechanism may also have first andsecond opposed interface surfaces having a spacing sufficiently smalltherebetween so as to act a barrier to inhibit the escape of lubricantin an inboard or outboard direction. As an example, the first, secondand third washers 245 a, 245 b or 245 c could be dimensioned to extendradially a sufficient extent to define only a small radial spacingbetween the two components, to inhibit lubricant from escaping.Alternatively, the sleeve portion 240 of the yoke 220 could extendfurther in the outboard direction, such that its radially inner surfaceopposes the radially outer surface of a shoulder portion 237 a of adriven drum 237.

First and second opposed interface surfaces further improve thecontainment of lubricant within the chamber. The surfaces may beradially opposed or axially opposed. The spacing required may be largerfor relatively viscous lubricants such as grease, and a closer fit forthinner.

When the adjuster mechanism 230 is assembled, the sleeve portion 240 ofthe yoke 220 is located concentrically between a wrap spring 239 and theinner piston 215 b. The sleeve portion 240 is restrained from rotating,as it is integral with, or secured to, the yoke 220, which is alsoconfigured to be non-rotatable when assembled in the disc brake.However, the inner piston 215 b is configured to rotate during anadjustment operation, to cause the piston 215 to advance in thedirection of the inboard brake pad. An outboard facing surface of theyoke 220 opposes and contacts an inboard facing end surface of the innerpiston 215 b. Friction between these two surfaces helps to inhibitundesired vibration-induced torque from affecting the adjustmentmechanism in operation, and causing undesired de-adjustment of the discbrake. Advantageously, the friction provides a consistent frictiontorque but in a small space envelope.

The two opposing surfaces are preferably arranged to have sufficientfriction to resist relative rotation of the yoke 220 and the innerportion 215 b of the piston 215 with a torque greater than the torquerequired to cause the one-way clutch of the adjuster mechanism (in thiscase the wrap spring 239) to slip when the actuation force is releasedat the end of a braking operation. This helps to ensure that the one-wayclutch slips rather than permits unwanted de-adjustment of the brakeoccurring during brake release. In this embodiment, the outboard facingsurface of the yoke of the piston is hardened. In alternativeembodiments, the inboard facing surface of the rotatable portion ishardened. It has been found that by hardening one of the two engagingsurfaces, undesirable fretting corrosion can be significantly reduced.

The first washer 245 a is located adjacent and inboard of a frictionclutch 241, and engages the friction clutch 241, as well as an outboardfacing surface of the stop 44. The second washer 245 b is locatedadjacent and outboard of the friction clutch 241, and an inboard surfaceof the second washer 245 b engages the friction clutch. An outboard faceof the second washer 245 b is acted on by a resilient element in theform, in this embodiment, of a compression spring 247. The compressionspring 247 is arranged concentrically within the inner piston 215 b,between the second washer 245 b and the third washer 245 c. In thisarrangement, an outboard face of the second washer 245 b is acted on bythe compression spring 247. The compression spring 247 acts as a clutchspring to load the friction clutch 241, to generate the required amountof friction to control the torque at which the friction clutch 241slips.

The compression spring 247 also controls the amount of friction betweenthe outboard facing surface of the yoke and the inboard facing endsurface of the inner piston 215 b. A force transmission path is definedfrom the compression spring 247 to the inner piston 215 b, to urge theinner piston 215 b into axial engagement with the yoke 220, to resistrelative rotation of the yoke 220 and the inner piston 215 b. It will beappreciated that a spring is just one type of biasing element that couldperform this function, and other biasing elements could also be used ifdesired.

This ‘face-to-face’ contact of the yoke 220 and inner piston 215 b,controlled by the compression spring 247, also helps to prevent leakageof lubricating fluid out of the chamber 270.

This adjuster mechanism 230 also makes it simple to define a chamber forlocating lubricating fluid that surrounds the wrap spring and frictionclutch, which are the components that are most in need of lubrication.

The compression spring 247 is pre-stressed by the stop 249 or end cap.In this embodiment, the stop 249 is generally hat-shaped incross-section, with a central bore so the stop 249 can be mounted on theprojecting portion 235 b of the drive drum 235. The stop 249 has asleeve portion projecting in an axially inboard direction. A secondrolling element bearing 218 b is provided between a radially outersurface of the sleeve portion of the stop 249 and a radially innersurface of the inner piston 215 b. In this embodiment the second rollingelement bearing 218 b is a thrust bearing that is arranged to isolatethe compression spring 247 and output clutch plates 241 b from the drivedrum 235 in rotation. The stop 249 engages the third washer 245 c viathe thrust bearing to pre-stress the compression spring 247. A clearanceexists between the cap and second bearing on the one hand, and the innerpiston on the other.

The arrangement of the second bearing 218 b also further assists toensure radial alignment in an angular sense (i.e., the drive drum, theyoke and the inner piston and inner piston remain co-axial) undereccentric loads from the operating shaft during an adjustment operation,and in particular during the return of the operating shaft and piston totheir brakes-off rest positions. The axial load from the compressionspring 247 (of the order of 600N) is transmitted to the projectingportion 235 b, the drive drum 235 and then into the yoke 220 by thefirst bearing 218 a. The compression spring also loads the inner piston215 b via the friction clutch 241 in the opposite direction. As such,even when return springs act on the yoke 220 and this in turn “pulls”the piston 215 back, the compression spring 247 load maintains full facecontact between the yoke 220 and the inner piston 215 b and with it theaxial alignment of the components.

In this embodiment, the outboard surface of the stop 249 is flush withthe outboard surface of the projecting portion 235 b of the drive drum235. This helps to ensure that the stop is mounted in the correctlocation during assembly of the adjustment mechanism. The stop 249 ismounted to the projecting portion 235 b with an interference fit. Itwill be appreciated in other embodiments that the stop 249 could bemounted differently e.g., with circlips or the like.

It will be appreciated that numerous changes may be made within thescope of the present invention. For example, certain aspects of theinvention may be applicable to other types of brake, such as twin pistonor electromechanically actuated brakes.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. An adjuster system for a disc brake, the adjustersystem comprising: a piston for applying an actuating force to a brakepad and being extensible to adjust a running clearance between a brakedisc and the brake pad, wherein the piston at least partially defines asingle chamber and has a stop that is disposed inside the chamber andthat extends in a radially inward direction; an operating shaft; and awear adjustment mechanism located within the chamber, for adjusting thepiston, the wear adjustment mechanism including: a one-way clutchconnected to the operating shaft; and a torque-limiting clutch; whereinthe adjuster system is configured to transfer any rotation of theoperating shaft beyond a predetermined degree to the one-way clutch, andthe torque-limiting clutch is configured to prevent extension of thepiston during a wear adjustment operation if a level of torque passingthrough the wear adjustment mechanism is higher than a predeterminedtorque value; and wherein the chamber is configured to contain lubricantfor lubrication of at least part of the wear adjustment mechanism and toinhibit lubricant from migrating away from the at least part of the wearadjustment mechanism, and the stop defines a barrier to inhibit escapeof the lubricant in an inboard or an outboard direction.
 2. The adjustersystem of claim 1 wherein the piston includes an outer piston and aninner piston that is received inside the outer piston, wherein the stopis integral with a radially inner surface of the inner piston.
 3. Theadjuster system of claim 1 wherein the wear adjuster mechanism has aradial step arranged to define a barrier to inhibit escape of thelubricant in an inboard or an outboard direction.
 4. The adjuster systemof claim 1 wherein the chamber and/or the wear adjustment mechanism hasfirst and second opposed interface surfaces having a spacingsufficiently small therebetween that acts as a barrier to inhibit escapeof lubricant in an inboard or an outboard direction.
 5. The adjustersystem of claim 1 wherein the chamber is provided as a unitary item withthe wear adjustment mechanism, such that the wear adjustment mechanismand the chamber are removeable together from a caliper housing.
 6. Theadjuster system of claim 1 wherein the stop provides a reaction surfacefor the torque-limiting clutch.
 7. The adjuster system of claim 6wherein the piston has inner and outer portions, wherein the outerportion includes a cap at an outboard end and a sleeve portionprojecting in an inboard direction from the cap, and wherein the innerportion and the wear adjustment mechanism are housed within the sleeveportion of the outer portion.
 8. The adjuster system of claim 7 whereinthe cap and the sleeve portion of the outer portion are integrally andmonolithically formed from a same piece of material.
 9. The adjustersystem of claim 7 wherein the cap extends transversely beyond the sleeveportion and provides a brake pad support arrangement to distribute theactuating force to the brake pad.
 10. The adjuster system of claim 9wherein the cap further comprises a brake pad mounting.
 11. The adjustersystem of claim 1 wherein the chamber is configured to hold apredetermined amount of lubricant for lubrication of the at least partof the wear adjustment mechanism in a substantially fluid-tight manner.12. The adjuster system of claim 1 wherein the chamber includes anopening at its inboard end, wherein loss of lubricant in an inboarddirection through the opening is inhibited by a sealing member that islocated within the chamber or immediately adjacent to the chamber. 13.The adjuster system of claim 12 further comprising a yoke arranged toactuate the piston, wherein the yoke has an axial bore that accommodatesat least a portion of the wear adjustment mechanism, and wherein thesealing member is located between a surface of the axial bore of theyoke and an opposing surface of a component of the wear adjustmentmechanism.
 14. The adjuster system of claim 13 wherein the wearadjustment mechanism comprises a drum configured to rotate as part of anadjustment operation, wherein the sealing member is located between thesurface of the axial bore of the yoke and the opposing surface is anopposing surface of the drum.
 15. The adjuster system of claim 12further comprising a yoke arranged to actuate the piston, wherein theyoke has an outboard projecting sleeve portion defining a portion of anaxial bore, and wherein the sealing member is located between a surfaceof the outboard projecting sleeve portion of the yoke and an opposingsurface of the piston.
 16. The adjuster system of claim 12 wherein thewear adjustment mechanism includes an axial bore and a manual adjustershaft assembly for manually retracting the piston through the axialbore, wherein the sealing member is located between a surface of theaxial bore and an opposing surface of the manual adjuster shaftassembly.
 17. The adjuster system of claim 16 wherein the surface of theaxial bore and the opposing surface of the manual adjuster shaftassembly are radially opposing surfaces.
 18. The adjuster system ofclaim 16 wherein: the sealing member is a lip seal or the sealing memberis an o-ring.
 19. An adjuster system for a disc brake, the adjustersystem comprising: a piston for applying an actuating force to a brakepad and being extensible to adjust a running clearance between a brakedisc and the brake pad; a single chamber that is at least partiallydefined by the piston; an operating, shaft: and a wear adjustmentmechanism located within the chamber, for adjusting the piston the wearadjustment mechanism including: a one-way clutch connected to theoperating shaft; and a torque-limiting clutch; wherein the adjustersystem is configured to transfer any rotation of the operating shaftbeyond a predetermined degree to the one-way clutch and the for thetorque-limiting clutch is configured to prevent extension of the pistonduring a wear adjustment operation if a level of torque passing throughthe wear adjustment mechanism is higher than a predetermined torquevalue; and wherein the chamber is configured to contain lubricant forlubrication of at least part of the wear adjustment mechanism and toinhibit lubricant from migrating away from the at least part of wearadjustment mechanism, and chamber comprises an aperture in a radiallyupper half of the piston for permitting passage of air into and out ofthe chamber.
 20. The adjuster system of claim 19 wherein the aperturecomprises a valve configured to permit air to pass through the aperture,but prevent fluid from passing through the aperture.
 21. A disc brakecomprising an adjuster system, the adjuster system comprising: a pistonfor applying an actuating force to a brake pad and being extensible toadjust a running clearance between a brake disc and the brake pad,wherein the piston at least partially defines a single chamber and has astop that is disposed inside the single chamber and that extends in aradially inward direction; an operating shaft; and a wear adjustmentmechanism located within the chamber, for adjusting the piston, the wearadjustment mechanism including: a one-way clutch connected to theoperating shaft; and a torque-limiting clutch; wherein the adjustersystem is configured to transfer any rotation of the operating shaftbeyond a predetermined degree to the one-way clutch, and thetorque-limiting clutch is configured to prevent extension of the pistonduring a wear adjustment operation if a level of torque passing throughthe wear adjustment mechanism is higher than a predetermined torquevalue; and wherein the chamber is configured to contain lubricant forlubrication of at least part of the wear adjustment mechanism and toinhibit lubricant from migrating away from the at least part of the wearadjustment mechanism, and the stop defines a barrier to inhibit escapeof the lubricant in an inboard or an outboard direction.